The present invention relates to fabrication of microelectronic components including components for connecting microelectronic devices with one another in service and test components used for testing other microelectronic devices.
Attempts have been made to make lead grid arrays by forming numerous leads at spaced locations on a metal sheet and bending the leads using a punch and die before attaching them to the components to be connected as shown, for example, in U.S. Pat. Nos. 5,420,461 and 5,210,939.
As disclosed, for example, in certain preferred embodiments of U.S. Pat. Nos. 5,518,964 and 5,798,286, the disclosures of which are hereby incorporated by reference herein and copies of which are annexed hereto, microelectronic components incorporating flexible leads can be made by a process in which the leads are connected between opposing elements and the opposing elements are moved away from one another so as to bend the leads through a controlled displacement. For example, in some embodiments taught by these patents, leads extend along the bottom surface of a dielectric connection component. Each lead has a terminal end connected to a metallic terminal which holds the terminal end of the lead in place. Each lead also has a tip end, remote from the terminal end, which is releasably held on the bottom surface of the dielectric element. The dielectric element is juxtaposed with another element, such as a semiconductor chip, wafer or additional connection component. The tip ends of the leads are bonded to contacts on the opposing element. The elements are then moved away from one another thereby detaching the tip end of each lead from the dielectric element and bending each lead to a vertically extensive disposition. A flowable material such as a curable dielectric liquid may be injected into the space between the leads during or after the movement step and cured to form a compliant dielectric layer surrounding the leads.
Numerous other variations and adaptations of the basic principles taught in these patents are also possible. For example, disclosed in co-pending, commonly assigned U.S. Provisional Patent Application No. 60/077,928, the disclosure of which is hereby incorporated by reference herein, the leads may be connected to one or another of the elements through frangible sections so that after the moving step, the frangible sections break leaving ends of the leads exposed at a surface of the dielectric layer formed from the encapsulant. Such a process can be used, for example, to fabricate test fixtures. As disclosed, for example, in co-pending, commonly assigned U.S. patent application Ser. No. 08/366,236, filed Dec. 29, 1994 and Ser. No. 08/989,312, filed Dec. 12, 1997, the disclosures of which are hereby incorporated by reference herein, one or another of the elements may include a metallic plate which is etched after the moving step to form terminals connected to the leads. However despite these and other advances in the art, still further variations would be desirable.
One aspect of the present invention provides a method of making a microelectronic unit. Methods according to this aspect of the invention desirably include the step of providing a grid formed from a flexible, electrically conductive material such a metal or metals. The grid has a bottom surface and a top surface and includes a plurality of elongated leads. Each lead has first and second ends. The grid further includes frangible elements connecting the first ends of at least some of the leads to the second ends of others of the leads. For example, some or all of the leads may arranged in an interspersed arrangement such that the first end of each such interspersed lead is disposed between the second ends of others of the interspersed leads, whereas the second end of each interspersed lead is disposed between the first ends of others of the interspersed leads.
The grid is placed between a top element and a bottom element so that the top surface of the grid faces toward the top element and the bottom surface of the grid faces toward the bottom element. The first ends of the leads are bonded to the top element but not the bottom element whereas the second ends of the leads are bonded to the bottom element but not to the top element. After bonding the leads to the top and bottom elements, the top and bottom elements are moved with a vertical component of motion away from one another so that the first ends of the leads move upwardly with respect to the second of the leads. During the moving step, the frangible elements connecting the first and second ends of the leads are broken and the leads end deformed to a vertically-extensive disposition. The element including the dielectric layer and the vertically extensive leads can be used, for example, as a connector which can be engaged between microelectronic elements to make temporary contacts during testing or to make permanent connections.
The grid may be provided with a bonding material on the top surface but not on the bottom surface at the first ends of the leads and with a bonding material on the bottom surface but not on the top surface at the second ends of the leads. The step of bonding the leads to the top and bottom element may include the step of activating these bonding materials. The top and bottom elements may include simple metallic plates, in which case the method desirably further includes the step of at least partially removing the metallic plates. Desirably, a flowable composition is injected around the leads as, for example, between the top and bottom elements during or after the step of moving the top and bottom elements away from one another and the flowable composition is cured to form a dielectric layers, such as a compliant gel or elastomer surrounding the leads.
During the moving step, portions of the frangible elements which remain attached to the first ends of the leads may be deformed downwardly relative to the first ends of the leads. These downwardly deformed portions of the frangible elements become embedded in the dielectric layer formed from the flowable composition and aid in anchoring the first ends of the leads to the dielectric layer. Similarly, portions of the frangible elements attached to the second ends of the leads project upwardly into the dielectric layer and also aid in anchoring the leads to the dielectric layer.
In further embodiments of the invention, one or both of the top and bottom elements may include preformed microelectronic elements having contacts thereon as, for example, a semiconductor chip or a dielectric layer with metallic contacts thereon. The bonding step is performed so as to align ends of leads with the contacts of the preformed elements and so as to connect the ends of the leads to such contacts.
In a further variant, the grid may include first conductors connected to the first ends of at least one of the leads. After the moving step, the first conductors extend at the level of the lead first ends. The first conductors may interconnect several lead first ends with one another so that when the component is engaged with a microelectronic element and the leads first ends are connected to contacts on the microelectronic element, the conductors interconnect the various contacts of the microelectronic element. Similarly, the grid may include one or more second conductors connected to the second ends of one or more of the leads, the second conductors remaining attached to the second ends of the leads after the moving step.
A further aspect of the invention provides a component for making a microelectronic assemblies. A component in accordance with this aspect of the invention includes a grid formed from a flexible electrically conductive material, the grid including plural leads each having a first end and a second end. Desirably, at least some of the leads are interspersed with one another so that the first end of each interspersed lead is disposed between the second ends of others of the interspersed leads and so that the second end of each interspersed leads is disposed between the first ends of other interspersed leads. The grid further includes frangible elements interconnecting the first and second ends of different leads to one another. The grid desirably includes bonding material as aforesaid on the top surface but not on the bottom surface of the grid at the first ends of the leads and on the bottom surface but not on the top surface at the second ends of the leads. Preferably, each of the leads is less than about 5 mm long and less than 100 mm wide. The leads may be considerably smaller than these dimensions components in accordance with these aspects of the invention can be utilized in processes as discussed above. The component may include first conductors connected to one or more of the first ends of the leads, second conductors connected to one another of the second ends of the leads, or both.